Seepage and stability of the colluvial landslide on the back hill of Qingshi Town Government under rainfall
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摘要: 以黄冈地区青石镇政府后山堆积层滑坡为例，在分析了其工程地质特征及地质结构特征的基础上，采用有限元法研究了非饱和土瞬态体积含水量及孔隙水压力的分布，采用考虑孔隙水压力的Janbu法分析计算了降雨对堆积层滑坡安全系数的影响。研究结果表明：①降雨入渗导致坡体孔隙水压力升高，滑面抗剪强度降低，安全系数也随之逐渐降低，其中在降雨前期，两侧的抗剪强度下降速率比中部快，而到了后期中部的抗剪强度下降速率明显快于两侧；②安全系数变化表现为前19 d以0.008/d的速率缓慢下降，19~30 d以0.03/d的速率缓慢下降，30 d以后下降速度降低，至36 d之后不再发生变化，其中在0~11 d两侧抗剪强度变化对滑坡整体稳定性变化的贡献比中部大，19~36 d中部抗剪强度变化对滑坡整体稳定性变化的贡献要比两侧大；③降雨入渗过程中，地下水从坡体表层和两侧流向坡体中部，负孔压区面积向中部不断压缩，中部地下水变化受到两侧及上层的制约，体积含水量及孔隙水压力变化相对滞后；④该滑坡的防治重点是做好降雨前期坡体后缘地下水截流以及前缘地下水排泄工作，同时，做好地表排水，减少降雨入渗。Abstract: Taking the colluvial landslide of the back hill of Qingshi Town Government in Huanggang area as an example, this paper used finite element method to study the transient volumetric water content and pore water pressure of unsaturated soil based on the analysis of its engineering geological characteristics and geological structure characteristics.The Janbu method considering pore water pressure was used to calculate the effect of rainfall on the safety factor of the colluvial landslide. The results show that:①Rainfall infiltration leads to the increase of pore water pressure in the slope, and then the shear strength of the sliding surface to decrease, and so the safety factor decreases gradually. In the early stage of rainfall, the shear strength on both sides decreases faster than that in the central part. At the end of the period, the rate of decline in shear strength is significantly faster than that on both sides.②The change in safety factor shows a slow decline at the rate of 0.008/d for the first 19 d and a slow decrease at the rate of 0.03/d for 19-30 d. After 30 d, the descending speed decreases, and no change occurres after 36 d. Among them, the change of shear strength on both sides of 0-11 d contributes more to the change of overall stability than that of the central part. The contribution of shear strength change to the overall stability of 19-36 d is greater than that of the central part.③During the rainfall infiltration, groundwater flows from the surface and sides of the slope to the middle of the slope, and the negative pore water pressure area is continuously compressed to the central part. The groundwater changes in the central area are restricted by the two sides and the upper layer. The volumetric water content and the pore water pressure change are relatively lagging.④The prevention and control of the landslide is focused on the groundwater interception at the trailing edge of the slope and the groundwater discharge at the leading edge. At the same time, a good surface drainage may reduce rainfall infiltration.
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Key words:
- colluvial landslide /
- rainfall /
- pore water pressure /
- shear strength /
- safety factor
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图 1 滑坡体全貌(a)及工程地质平面图(b)
1.滑坡边界；2.裂缝；3.滑坡堆积体；4.太古宇大别山群；5.剖面线及编号；6.钻孔编号及高程(m)
Figure 1. Overall view of the landslide (a) and engineering geological plan (b)
图 3 Janbu法微分土条受力示意图
Wi为土条i的重力(kN)；Hi，Hi+1分别为土条i两侧的切向力；pi、pi+1分别为土条i的两侧法向力(kN)；θi为土条i滑面倾角(°)；Ni为土条i的支持力(kN); Ti为土条i的下滑力(kN)
Figure 3. Schematic diagram of the differential force of the Janbu method
图 7 降雨3 d的数值模拟
a.降雨3 d后体积含水量分布; b.降雨3 d后孔隙水压力分布
Figure 7. Numerical simulation of rainfall 3 d
图 8 降雨11 d的数值模拟
a.降雨11 d后体积含水量分布; b.降雨11 d后孔隙水压力分布
Figure 8. Numerical simulation of rainfall 11 d
图 9 降雨19 d的数值模拟
a.降雨19 d后体积含水量分布; b.降雨19 d后孔隙水压力分布
Figure 9. Numerical simulation of rainfall 19 d
图 10 降雨36 d的数值模拟
a.降雨36 d后体积含水量分布; b降雨36 d后孔隙水压力分布
Figure 10. Numerical simulation of rainfall 36 d
图 11 降雨50 d的数值模拟
a.降雨50 d后体积含水量分布; b.降雨50 d后孔隙水压力分布
Figure 11. Numerical simulation of rainfall 50 d
图 12 体积含水量和孔隙水压力与降雨时间的关系
a.体积含水量与降雨时间的关系; b.孔隙水压力与降雨时间的关系
Figure 12. Volume moisture content and pore water pressure relationship with the rainfall time respectively
图 13 监测点所在条块抗剪强度随降雨时间的变化关系图
Figure 13. Relationship between shear strength of monitoring points and rainfall time
图 15 各时间段抗剪强度与安全系数的变化对照图
Figure 15. Comparison of changes in shear strength and safety factor for each time period
表 1 渗流计算参数
Table 1. Parameters of seepage calculation
位置 饱和体积含水量/(m3·m-3) 饱和渗透系数/(m·s-1) 滑体 0.4 1.0×10-6 
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表 2 岩土体物理力学参数
Table 2. Physical and mechanical parameters of rock and soil
岩性 重度/ (kN·m-3) 有效黏聚力/kPa 有效内摩擦角/(°) 吸力内摩擦角/(°) 粉质黏土夹碎石 20.1 21 24 15 中风化黑云斜长片麻岩 28.18 10 200 47
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